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Complexes of Ras.GTP with Raf-1 and mitogen-activated protein kinase kinase
S A Moodie1, B M Willumsen, M J Weber
1Department of Cell Biology, Cleveland Clinic Foundation, OH 44106.
Abstract:
The guanosine triphosphate (GTP)-binding protein Ras functions in regulating growth and differentiation; however, little is known about the protein interactions that bring about its biological activity. Wild-type Ras or mutant forms of Ras were covalently attached to an insoluble matrix and then used to examine the interaction of signaling proteins with Ras. Forms of Ras activated either by mutation (Gly12Val) or by binding of the GTP analog, guanylyl-imidodiphosphate (GMP-PNP) interacted specifically with Raf-1 whereas an effector domain mutant, Ile36Ala, failed to interact with Raf-1. Mitogen-activated protein kinase (MAP kinase) activity was only associated with activated forms of Ras. The specific interaction of activated Ras with active MAP kinase kinase (MAPKK) was confirmed by direct assays. Thus the forming of complexes containing MAPKK activity and Raf-1 protein are dependent upon the activity of Ras.
Insights
Activated Ras signaling proteins specifically bind to Raf-1 and MAP kinase kinase (MAPKK). This interaction is crucial for regulating cell growth and differentiation, highlighting Ras
Area of Science:
- Cellular signaling and molecular biology.
- Investigating the role of guanosine triphosphate (GTP)-binding proteins in cellular processes.
Background:
- The guanosine triphosphate (GTP)-binding protein Ras is vital for regulating cell growth and differentiation.
- The specific protein interactions mediating Ras' biological activity remain largely uncharacterized.
Purpose of the Study:
- To elucidate the protein interactions involved in Ras-mediated cellular signaling.
- To identify the specific binding partners of activated Ras.
Main Methods:
- Covalent attachment of wild-type and mutant Ras proteins to an insoluble matrix.
- Affinity assays to examine the interaction of signaling proteins with immobilized Ras.
- Direct assays to confirm interactions between Ras and MAP kinase kinase (MAPKK).
Main Results:
- Activated forms of Ras (mutant Gly12Val or bound to GMP-PNP) specifically interacted with Raf-1.
- An effector domain mutant (Ile36Ala) failed to interact with Raf-1.
- Mitogen-activated protein kinase (MAP kinase) activity was exclusively associated with activated Ras.
- Direct assays confirmed the specific interaction between activated Ras and active MAP kinase kinase (MAPKK).
Conclusions:
- The formation of protein complexes involving MAPKK activity and Raf-1 is dependent on Ras activity.
- Activated Ras directly interacts with Raf-1 and MAPKK, suggesting a key role in signal transduction pathways.
- These findings provide critical insights into the molecular mechanisms governing Ras-driven cellular processes.